The present invention relates to a process for the treatment of lignocellulose materials, in particular wood, and to a material obtained by this process.
It is targeted more particularly at a process for protecting wood which makes it possible to confer a hydrophobic nature on it, in order to enhance its durability and its dimensional stability.
It is known that, in the natural state, wood or more specifically food fibers which are in contact with a wet atmosphere have a tendency to soak up water. This absorption of water is accompanied by swelling.
Drying can be carried out to remove this water. However, although the drying stage makes it possible to remove the water from the wood, it does not in any way modify its natural hydrophilic nature, with the result that the piece of wood is again capable of reabsorbing the water removed during the drying when this piece is again in a wet environment.
In order to reduce, indeed even eliminate, the hydrophilic nature of the wood and thus to confer on it long-term (conventionally about ten years) dimensional stability, treatment techniques have been sought.
Among these, two main families may be noted, which families are differentiated into physical processes of heat treatment (generally at temperatures of greater than 150° C.) and physicochemical treatment processes, generally at temperatures of less than 120° C.
The present invention is concerned with physicochemical treatment processes.
These physicochemical treatments include processes, known in particular from several publications, Arni et al., (Arni, 1961) ; Matsuzaki et al., which make it possible to synthesize mixed esters from a trifluoroacetic medium. These processes are not viable industrially because of the use of toxic solvent and toxic catalyst.
Additional studies carried out on wood sawdust have demonstrated that the esterification in the presence of a strong acid catalyst (adding more to the intrinsic acidity of the medium) makes it possible to confer a hydrophobic nature on this sawdust. These studies formed the subject of the following publication: Vaca-Garcia C. and Borredon M. E., 1999, Solvent-free fatty acylation of cellulose and lignocellulosic wastes. Part 2: reactions with fatty acids, Bioresource Technology, 70, 135-142.
The major disadvantages [lacuna] this process in the presence of an acid catalyst are the loss in mass of the wood sawdust, this loss in mass resulting from decomposition of the biopolymers constituting the sawdust. A change in color of the sawdust after treatment may also be observed.
A technique similar to the above cannot be applied to a piece of wood. This is because it has been found that hemicellulose molecules and cellulose are partially hydrolyzed, which results in a decrease in the molecular weight through the formation of oligomers and in a decline in the mechanical properties, and also in a deterioration in the appearance of the treated piece of wood.